A Simple Voltage Balancing Scheme for m-Level Diode-Clamped Multilevel Converters Based on a Generalized Current Flow Model

Abstract

This paper presents a simple voltage balancing scheme for m-level diode-clamped multilevel converters (DCMC). This paper first introduces a novel and simple current flow model for general m -level DCMCs. The superiority of the proposed model is its independence from the modulation scheme and its simplicity. It also provides a new perspective for voltage sharing accessibility among the dc link capacitors. The proposed current flow model, a cost function, and a space vector modulation (SVM) switching strategy are then used to balance the capacitors' voltages of the DCMCs in a very simple and optimized manner. Such a voltage balancing scheme was not developed for converters of five levels or greater due to the complexity of the converter and its modeling approaches. To validate the feasibility of the proposed voltage balancing scheme, this paper presents analytical and simulation results obtained from a five-level DCMC. In particular, this paper introduces a stability region within which the voltage balancing strategy converges. The impact of the cost function on the stability margins and converter performance is examined and discussed by means of comparison with different cost functions, and it is shown that the proposed cost function will improve the stability margins. The performance of the strategy for unbalanced and polluted loads shows that, unexpectedly, in some specific cases output current harmonics will improve the stability margin.